The present invention relates to an injector mechanism used to demist and defog the hood and visor of an aircrew chemical and biological warfare ("CBW") respirator system.
Currently, most aircrew CBW respirator systems utilize either a motor driven filter-blower, or 100 percent breathing gas to supply the gas flow to demist and defog the aircrew respirator hood and visor assembly. Each of these methods has certain drawbacks.
The use of a motor driven filter-blower unit is useful in providing a safe source of breathing and demist gas while the aircrew is entering and exiting the aircraft. However, once the aircrew is in the aircraft, a filter-blower is cumbersome to stow in the cockpit during flight and has a limited battery life. Also, a filter-blower can only be used to supply breathing gas if the aircraft is scheduled for a mission below an altitude of about 10,000 feet since filtered cabin air does not contain a sufficient oxygen concentration for prolonged aircrew breathing at the higher altitudes.
A second method uses 100 percent breathing gas (oxygen) for demist and defog purposes. This consumes the liquid oxygen ("LOX") or high pressure gaseous oxygen ("GOX") breathing gas supply and can result in a restricted flight duration capability for the aircraft. Using 100 percent breathing gas for demist and defog from an on board oxygen generating system ("OBOGS") equipped aircraft does not limit the flight duration because of the unlimited supply available. However, it requires the OBOGS to be considerably larger in order to accommodate the demist flow requirements while maintaining the required breathing gas at minimum oxygen concentration levels.
One prior art system shown in U.S. Pat. No. 4,741,332 uses an injector to entrain cabin air which is drawn through a CBW filter and used for demist and defog purposes The injector is downstream of the CBW filter; however, and the negative pressure (suction) which is created by the injector allows the possibility of inward chemical agent leakage at the junctions of system components with resulting contamination of the demist and defog gas stream.
It would, accordingly, be desirable to provide a demist system to provide physiologically safe oxygen demist and breathing gas while minimizing the demand on the oxygen supply source so as to not reduce the flight capability of the aircraft or require an oxygen supply system having substantially greater capacity. It would be further desirable to provide an injector to entrain cabin air for demist purposes which did not create negative pressure downstream of the CBW filter and the possibility of inward chemical agent leakage.